This invention relates to turbochargers and, more particularly, to a unique water-cooled bearing housing for a turbocharger.
The present invention concerns a water-cooled turbocharger that has important performance and manufacturing advantages over the existing prior art.
Conventionally designed turbochargers used in automotive and other high temperature applications have been experiencing an increasingly high failure rate due to an phenomenom known as "oil coking". This occurs after the engine is shut down and the heat stored up in the exhaust manifold and turbine housing soaks back into the turbocharger bearing housing. The bearing housing temperature increases until it reaches the temperature required to burn oil. Any oil remaining in the bearing housing is then burned into a thin film of "coke". This process continues until the accumulation of coke deposits completely plugs up the small oil passages. This results in oil starvation to the bearings and then complete failure of the turbocharger rotating assembly.
This problem has been addressed in previous art by using water to cool the bearing housing to prevent it from reaching the temperature required to burn oil. This has been accomplished by casting a water passage into the bearing housing and then circulating engine cooling water through the passage. Prior art designs have used passages that were completely contained within the bearing housing casting. This design requires a casting process with a core, and therefore limits the castings options accordingly.
One important casting method that cannot be easily used with the prior designs is die casting. Die casting has several manufacturing advantages when used to make turbocharger bearing housings. Aluminum die casting housings have excellent heat transfer characteristics, thereby allowing faster heat transfer of the heat around the bearings to the water passage. Die casting is one of the most economical methods of casting. Die cast parts are also near net shape and can be easily designed for a minimum of machining operations, thereby further reducing the cost of the finished part when compared to parts that are cast by a casting process that requires a core.
A need remains to provide a water-cooled turbocharger bearing housing that may be die cast without a core.